Bacteria and Viruses Overview

Bacteria and Viruses

• Bacteria are single-celled prokaryotic organisms. They lack a membrane-bound nucleus and other membrane-bound organelles.
• Viruses are acellular entities, meaning they are not composed of cells. They are essentially genetic material (DNA or RNA) enclosed in a protein coat. They require a host cell to replicate.
• Bacteria and viruses are both significant agents of disease, but through vastly different mechanisms.

Bacterial Structure

• Bacteria possess a cell wall composed primarily of peptidoglycan. This rigid structure provides shape and protection (important for Gram staining).
• Different bacterial species can be classified based on the thickness and composition of their cell walls. Gram-positive bacteria have a thick peptidoglycan layer, while gram-negative bacteria have a thin peptidoglycan layer surrounded by an outer membrane.
• Some bacteria have flagella for motility, pili for attachment, and capsules for protection.
• Internal structures include ribosomes for protein synthesis and plasmids for extrachromosomal DNA.

Viral Replication

• Viral replication involves the following steps:
  • Attachment: The virus attaches to specific receptors on the host cell surface.
  • Entry: The viral genome enters the host cell.
  • Replication: The viral genome is replicated using the host cell's machinery.
  • Assembly: New viral components are assembled to form new virus particles.
  • Release: The newly assembled viruses are released from the host cell, often causing cell lysis (destruction).
• Different viruses employ different mechanisms for each replication step.
• Viruses can cause acute, chronic, or latent infections depending on how they interact with the host cells.

Antibiotic Resistance

• Antibiotic resistance is the ability of bacteria to survive and reproduce in the presence of antibiotics.
• Antibiotic resistance is a major threat to public health.
• Resistance arises from genetic mutations in bacterial DNA, often acquired through horizontal gene transfer (e.g., plasmids).
• Overuse and misuse of antibiotics contribute significantly to the rise of antibiotic resistance.
• Preventing the development and spread of antibiotic resistance requires responsible antibiotic use, and the development of new antibiotics.

Immune Response

• The immune system plays a crucial role in defending the body against pathogens, including bacteria and viruses.
• The immune response involves various components and mechanisms that work in concert to eliminate or neutralize pathogens.
• The innate immune response provides immediate, non-specific defenses. This includes physical barriers, phagocytes (cells that engulf and destroy pathogens), and inflammation.
• The adaptive immune response provides a more specialized and long-lasting defense. It involves lymphocytes, including B cells and T cells, that recognize specific antigens (molecules on the surface of pathogens).
• B cells produce antibodies that mark pathogens for destruction.
• T cells have diverse roles, from direct killing of infected cells to aiding other immune responses.
• Memory cells provide immunological memory, promoting faster and stronger responses to subsequent exposures to the same pathogen.

Pathogenic Mechanisms

• Bacteria can cause disease through several mechanisms, including:
  • Toxin production: Some bacteria release toxins that damage host tissues (e.g., exotoxins and endotoxins).
  • Invasion: Certain bacteria can invade tissues and spread throughout the body (e.g., by producing enzymes that degrade the extracellular matrix).
  • Inflammation: Pathogens trigger an inflammatory response that can be detrimental if excessive (e.g., septic shock).
• Viruses cause disease by:
  • Damaging host cells directly.
  • Activating the immune system, which may contribute to the disease.
• The severity of the disease often depends on the pathogen's virulence, which is its ability to cause disease, and the host's immune response.

This quiz covers the fundamental concepts of bacteria and viruses, including their structures, classifications, and mechanisms of disease. Learn about the distinctive characteristics that differentiate these two types of microorganisms and their impact on health.